Display device and method for driving the same

ABSTRACT

In order to display 3D images by a parallax barrier method, a display screen and the eyes of a viewer need to have a specific positional relation. An object is to provide a display device with an extended area where the viewer can perceive 3D images with the naked eye. Attention is focused on the position of the viewer with respect to pixels provided in a display device and a mode of a parallax barrier provided between the viewer and the pixels. This leads to a structure in which the position of the viewer with respect to pixels is specified by using an ultrasonic wave to change a mode of a parallax barrier in accordance with the position of the viewer, thereby achieving the above object.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and a method fordriving the display device, and particularly to a display device capableof displaying three-dimensional (3D) images and a method for driving thedevice capable of displaying 3D images.

2. Description of the Related Art

A variety of display devices ranging from large display devices such astelevision devices to small display devices such as mobile phones areput on the market.

High value-added products will be needed and are being developed. Inrecent years, display devices that can display 3D images have beendeveloped in order to display more realistic images.

As methods for displaying 3D images, there are a method using glassesfor separating an image seen with a left eye and an image seen with aright eye (also referred to as stereoscopy or image separation method),and autostereoscopy (a naked eye method) by which 3D images can be seenby the naked eye by addition of a structure for separating an image seenwith a left eye and an image seen with a right eye in a display portion.It is not necessary to prepare glasses to see autostereoscopic 3Dimages, which offers a high convenience. Autostereoscopic 3D display iscoming into widespread use such as mobile phones and mobile gameconsoles.

As a method for displaying autostereoscopic 3D images, there is known aparallax barrier method in which a parallax barrier is added to adisplay portion. A parallax barrier for this method is a stripe-shapedlight-shielding portion and causes a decrease in resolution when displayis switched from 3D display to 2D display. In view of this, for aparallax barrier method, there is suggested a structure in which aliquid crystal panel having a patterned transparent electrode is used,and when display is switched between 2D display and 3D display,transmission or shielding of light by a liquid crystal layer iscontrolled by controlling voltage applied to the transparent electrodein order to set the presence or absence of a parallax barrier (seePatent Document 1).

REFERENCE

Patent Document 1: Japanese Published Patent Application No. 2005-258013

SUMMARY OF THE INVENTION

However, in order to display 3D images by a parallax barrier method, adisplay screen and the eyes of a viewer need to have a specificpositional relation.

<Problem Caused When Viewer is Closer to 3D Display Device>

A description is given with reference to FIG. 10A of the position of theeyes of a viewer with respect to pixels and a mode of a parallax barrierprovided between the viewer and the pixels at the time of displaying 3Dimages by a parallax barrier method. FIG. 10A schematically illustratesthe viewpoint of the viewer and cross sections of a display panel 700and a parallax barrier 690, which are cut along a plane passing throughthe right and left eyes of the viewer. In the parallax barrier,light-transmitting regions and light-blocking regions are alternatelyarranged, and the parallax barrier is mainly stripe-shaped. Note thatFIG. 10A shows the cross section of the stripe-shaped parallax barrier.The display panel 700 includes a first pixel region 710 for a left eye10L and a second pixel region 720 for a right eye 10R, and the parallaxbarrier 690 is placed between the first pixel region 710 and the righteye 1OR and between the second pixel region 720 and the left eye 10L.With such a positional relation, the parallax barrier 690 serves as a“blindfold” for the right and left eyes. As a result, the viewer seesthe first pixel region 710, where a left-eye image is displayed, withthe left eye 10L and the second pixel region 720, where a right-eyeimage is displayed, with the right eye 1OR and thus perceives 3D images.In FIG. 10A, an image perceived by the right eye 1OR of a viewer 10 isshown above the right eye 1OR and an image perceived by the left eye 10Lis shown above the left eye 10L.

Next, the case where the viewer is closer to the display panel will bedescribed with reference to FIG. 10B. If the viewer is closer to thedisplay panel, the left eye 10L sees part of the second pixel region 720adjacent to the first pixel region 710 and the right eye 10R sees partof the first pixel region 710 adjacent to the second pixel region 720.Consequently, the viewer sees part of an image for the right eye 10R,which is not supposed to be seen with the left eye 10L, and part of animage for the left eye 10L, which is not supposed to be seen with theright eye 10R; therefore, it becomes difficult for the viewer toperceive 3D images. In FIG. 10B, an image perceived by the right eye 10Rof the viewer 10 is shown above the right eye 10R and an image perceivedby the left eye 10L is shown above the left eye 10L. Note that aphenomenon in which one eye of the viewer sees part of an image for theother eye, which is not supposed to be seen with the one eye, is calledcrosstalk in this specification.

<Problem Caused When Viewer Moves Along 3D Display Device>

Next, a description is given with reference to FIGS. 11A and 11B of thedifference between a mode of a parallax barrier that overlaps an outeredge portion of the display panel and a mode of a parallax barrier thatoverlaps a center portion of the display panel. The display panel 700 isa 3D display device used in such a manner that the viewer 10 faces thecenter portion (represented by an arrow in the drawing for convenience).In the center portion, the parallax barrier is formed so that its centeris aligned with the boundary between a pixel for the right eye and apixel for the left eye that are adjacent to each other. In the centerportion of the display panel 700 in FIG. 11A, a pixel for the left eye10L included in the first pixel region 710 and a pixel for the right eye1OR included in the second pixel region 720 are shown. When focusing ona trapezoid where a pair of pixels one of which is for the right eye andthe other of which is for the left eye (hereinafter “a pair of right-eyeand left-eye pixels”) is treated as the lower base and a light-blockingportions in a parallax barrier therefor as the upper base, the trapezoid(represented by a dense hatch pattern in the drawing) is symmetrical inthe center portion of the display panel 700.

However, as a parallax barrier is farther from the center portion of thedisplay panel 700 and closer to the outer edge portion, it is madecloser to the viewer (i.e., the center portion of the panel), beingmoved from a portion directly above the boundary where the first pixelregion 710 and the second pixel region 720 are in contact with eachother. This is because the viewer positions themselves to see thedisplay panel from an oblique direction; therefore, if a parallaxbarrier is formed so that its center can be aligned with the boundarybetween the pixel for the right eye and the pixel for the left eye, theviewer sees part of an image for the right eye 10R, which is notsupposed to be seen with the left eye 10L, and part of an image for theleft eye 10L, which is not supposed to be seen with the right eye 10R.Thus, it becomes difficult for the viewer to perceive 3D images. Forthat reason, a parallax barrier is provided so that, as the parallaxbarrier is farther from the center portion of the display panel 700 andcloser to the outer edge portion, the trapezoid (a pair of right-eye andleft-eye pixels is treated as the lower base and a light-blockingportions in a parallax barrier therefor as the upper base) falls towardthe center portion of the display panel 700 and is distorted.

A description is given with reference to FIG. 11B of the case where theviewer 10 moves from the center portion along the display panel in the3D display device having the above structure. When focusing on thetrapezoid (a pair of right-eye and left-eye pixels is treated as thelower base and a light-blocking portions in a parallax barrier thereforas the upper base) at the front of the viewer 10 who has moved to right,the trapezoid falls toward the center portion of the display panel 700and is distorted. Consequently, the viewer sees part of an image for theright eye 10R, which is not supposed to be seen with the left eye 10L,and part of an image for the left eye 10L, which is not supposed to beseen with the right eye 10R; thus, it becomes difficult for the viewerto perceive 3D images. As above, in order to display 3D images by aparallax barrier method, the display screen and the eyes of the viewerneed to have a specific positional relation.

An embodiment of the present invention is made in view of the foregoingtechnical background. Therefore, an object of one embodiment of thepresent invention is to provide a display device with an extended areawhere a viewer can perceive 3D images with the naked eye. Another objectof one embodiment of the present invention is to provide a method fordriving a display device with an extended area where a viewer canperceive 3D images with the naked eye.

In order to achieve the above objects, in one embodiment of the presentinvention, attention is focused on the position of a viewer with respectto pixels provided in a display device and a mode of a parallax barrierprovided between the viewer and the pixels. This leads to a displaydevice having a structure exemplified in this specification. Accordingto one embodiment of the present invention, the position of a viewerwith respect to pixels is specified by using an ultrasonic wave tochange a mode of a parallax barrier in accordance with the position ofthe viewer.

That is, one embodiment of the present invention is a display devicethat includes a display panel including a first pixel region for a lefteye and a second pixel region for a right eye; a parallax barrier thatcovers part of the display panel and is variable in mode; a parallaxbarrier control circuit configured to control a mode of the parallaxbarrier; a plurality of detectors; and an ultrasonic generator. Theparallax barrier control circuit controls the parallax barrier inaccordance with the position of the viewer specified by the plurality ofdetectors such that the parallax barrier prevents the right eye of theviewer from seeing the first pixel region and the left eye of the viewerfrom seeing the second pixel region.

In the display device according to one embodiment of the presentinvention, the mode of the parallax barrier is changed in accordancewith the position of the viewer specified by the plurality of detectorsand the ultrasonic generator with respect to pixels. Thus, the positionof the right eye and left eye of the specified viewer with respect toeach of the pixels included in the display device can be found.Consequently, it is possible to provide a display device with anextended area where the specified viewer can perceive 3D images with thenaked eye. Further, since an ultrasonic wave is used, the position ofthe viewer can be accurately detected even in a dark environment. As aresult, the viewer can perceive brighter and clearer 3D display images.

Another embodiment of the present invention is a display device whichhas the above-described structure and in which the parallax barrier isformed using a liquid crystal layer sandwiched between a pair ofsubstrates, and at least one of the pair of substrates is provided witha plurality of electrodes for controlling alignment of liquid crystalsin the liquid crystal layer and each of the plurality of electrodes iselectrically connected to the parallax barrier control circuit.

In the display device according to one embodiment of the presentinvention, a parallax barrier is provided with a liquid crystal layerand a plurality of electrodes for controlling alignment of liquidcrystals in the liquid crystal layer, and each of the electrodes iselectrically connected to the parallax barrier control circuit. Thus,the mode of the parallax barrier can be changed in accordance with theposition of the viewer by using the parallax barrier control circuit sothat the parallax barrier can block the right eye of the viewer fromseeing the first pixel region and the left eye of the viewer from seeingthe second pixel region. It is therefore possible to provide a displaydevice with an extended area where the viewer can perceive 3D imageswith the naked eye.

Another embodiment of the present invention is a method for driving adisplay device including the following six steps. In the first step, apulsed ultrasonic wave is transmitted towards the space in front of aside where a display surface of the display device faces a viewer. Inthe second step, the presence or absence and position of the viewer isspecified by using a time it takes for a reflected pulsed ultrasonicwave to reach each of a plurality of detectors. In the third step, apair of right-eye and left-eye pixels facing a front of the viewer isspecified by calculating coordinates where a straight line passingthrough the position of the viewer orthogonally crosses the displaysurface. In the fourth step, a distance from the pair of right-eye andleft-eye pixels to the viewer is specified. In the fifth step, the sizeof a parallax barrier corresponding to the pair of right-eye andleft-eye pixels is controlled with reference to the distance from thepair of right-eye and left-eye pixels to the viewer so that a right eyeof the viewer sees the pixel for the right eye and a left eye of theviewer sees the pixel for the left eye. In the sixth step, a parallaxbarrier is formed so that a trapezoid in which another pair of right-eyeand left-eye pixels is treated as a lower base and a light-blockingportions in a parallax barrier therefor as an upper base falls towardthe viewer and is further distorted as the trapezoid is more distantfrom the pixels facing the front of the viewer in a horizontaldirection, and so that the parallax barrier prevents the left eye of theviewer from seeing a pixel region for the right eye and the right eye ofthe viewer from seeing a pixel region for the left eye.

According to the method for driving the display device in one embodimentof the present invention, the mode of the parallax barrier can bechanged in accordance with the position of the specified viewer by usingthe parallax barrier control circuit so that the parallax barrier canprevent the right eye of the viewer from seeing the first pixel regionand the left eye of the viewer from seeing the second pixel region.Consequently, it is possible to provide the method for driving thedisplay device with an extended area where the specified viewer canperceive 3D images with the naked eye.

According to one embodiment of the present invention, it is possible toprovide a display device with an extended area where the specifiedviewer can perceive 3D images with the naked eye. According to anotherembodiment of the present invention, it is possible to provide a methodfor driving a display device with an extended area where the specifiedviewer can perceive 3D images with the naked eye.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate positions of a display device according to anembodiment and a user, and a configuration of the display device;

FIGS. 2A and 2B illustrate the relation between a mode of a parallaxbarrier and the distance between a display panel according to anembodiment and a viewer;

FIGS. 3A and 3B illustrate the relation between a mode of a parallaxbarrier and the position of a viewer moving along a display panelaccording to an embodiment;

FIGS. 4A1, 4A2, 4B1, and 4B2 illustrate parallax barriers according toan embodiment;

FIG. 5 illustrates a parallax barrier according to an embodiment;

FIGS. 6A and 6B illustrate a display panel according to an embodiment;

FIGS. 7A and 7B illustrate a display panel according to an embodiment;

FIGS. 8A and 8B illustrate a shutter panel including a touch panelaccording to an embodiment;

FIGS. 9A to 9C each illustrate an electronic device according to anembodiment;

FIGS. 10A and 10B illustrate a conventional technique;

FIGS. 11A and 11B illustrate a conventional technique;

FIG. 12 is a block diagram illustrating a 3D display device according toan example;

FIGS. 13A-L, 13A-R, and 13B show a method for evaluating a 3D displaydevice according to an example;

FIG. 14 shows results of evaluating a 3D display device according to anexample;

FIG. 15 shows results of evaluating a 3D display device according to acomparative example;

FIG. 16 shows characteristics of a transistor; and

FIGS. 17A to 17D are diagrams for explaining an ultrasonic sensor.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to theaccompanying drawings. Note that the present invention is not limited tothe following description, and it is easily understood by those skilledin the art that various changes and modifications can be made withoutdeparting from the spirit and scope of the present invention. Therefore,the present invention is not supposed to be construed as being limitedto the description in the following embodiments. Note that in thestructures of the invention described below, the same portions orportions having similar functions are denoted by the same referencenumerals in different drawings, and description of such portions is notrepeated.

Embodiment 1

In this embodiment, a description is given with reference to FIGS. 1Aand 1B, FIGS. 2A and 2B, and FIGS. 3A and 3B of a display device inwhich the position of a viewer with respect to pixels is specified byusing an ultrasonic wave to change a mode of a parallax barrier inaccordance with the position of the viewer. Specifically, a descriptionis given of a display device that includes a display panel including afirst pixel region and a second pixel region; a parallax barrier thatcovers part of the display panel and is variable in mode; a parallaxbarrier control circuit for controlling the mode of the parallaxbarrier; a plurality of detectors; and an ultrasonic generator. In thedisplay device, the parallax barrier control circuit controls theparallax barrier in accordance with the position of the viewer specifiedby the plurality of detectors such that the parallax barrier preventsthe right eye of the viewer from seeing the first pixel region and theleft eye of the viewer from seeing the second pixel region.

<Structure of Display Device>

FIG. 1A shows the positions of a display device 20 according to oneembodiment of the present invention and a viewer 10 that uses thedisplay device 20. The viewer 10 uses the display device 20 while facinga display surface.

The display device 20 includes a display panel 200, a shutter panel 100in which a parallax barrier is formed on the display surface side of thedisplay panel 200, and a control device 30. The display device 20 isprovided with an ultrasonic generator 161 and detectors 162R and 162L,which are positioned so that a reflected wave of an ultrasonic waveemitted from the ultrasonic generator 161 toward the viewer 10 isreceived by the detectors.

The control device 30 will be described in detail with reference to ablock diagram illustrated in FIG. 1B. The control device 30 includes aviewer detection circuit 160, an image signal generation circuit 260, aparallax barrier control circuit 150, and a display panel driver circuit250. The image signal generation circuit 260 is electrically connectedto the display panel 200 through the display panel driver circuit 250and electrically connected to the shutter panel 100 through the parallaxbarrier control circuit 150. The ultrasonic generator 161 and thedetectors 162R and 162L are connected to the viewer detection circuit160. The viewer detection circuit 160 is electrically connected to theparallax barrier control circuit 150 and the image signal generationcircuit 260.

The image signal generation circuit 260 converts image data stored in astorage medium and image data input from an external device connected tothe control device 30 into an image signal with which the display deviceexemplified in this embodiment can display images, and outputs the imagesignal. Moreover, the image signal generation circuit 260 varies animage signal, for example, in accordance with a signal that is outputfrom the viewer detection circuit 160 and specifies the position of theviewer. Specifically, the position of the eyes of the viewer isestimated from the position of the viewer facing the display panel 200,the mode of the parallax barrier is determined so that the viewer caneasily perceive 3D images, and a parallax barrier control signal isoutput to the parallax barrier control circuit 150 to achieve thedetermined mode of the parallax barrier.

Further, the image signal generation circuit 260 can vary an imagesignal output from a game console in accordance with locationinformation of the viewer, for example. For instance, the story line ofa video game may be selected from several options in accordance with theposture of a viewer detected.

The parallax barrier control circuit 150 drives the shutter panel 100 inaccordance with a parallax barrier control signal output from the imagesignal generation circuit 260 to change the mode of the parallaxbarrier.

The display panel driver circuit 250 drives the display panel 200 inaccordance with an image signal output from the image signal generationcircuit 260 to display images.

<Method for Driving Display Device>

A method for driving the display device 20 according to one embodimentof the present invention will be described. The display device 20operates by repeating the following six steps.

In the first step, the ultrasonic generator 161 transmits a pulsedultrasonic wave to the display surface side. In the second step, thepresence or absence and position of a viewer are specified using thetime it takes for a reflected pulsed ultrasonic wave to reach each ofthe plurality of detectors.

In the subsequent third step, the image signal generation circuit 260calculates coordinates where a straight line passing through theposition of the viewer orthogonally crosses the display surface, tospecify a pair of right-eye and left-eye pixels facing the front of theviewer. Then, in the fourth step, the image signal generation circuit260 specifies the distance from the pair of right-eye and left-eyepixels to the viewer.

Next, in the fifth step, the image signal generation circuit 260controls the size of a parallax barrier corresponding to the pair ofright-eye and left-eye pixels via the parallax barrier control circuit150 with reference to the distance from the pair of right-eye andleft-eye pixels to the viewer so that the right eye of the viewer cansee the pixel for the right eye and the left eye of the viewer can seethe pixel for the left eye.

In the sixth step, the image signal generation circuit 260 forms theparallax barrier via the parallax barrier control circuit 150 so that atrapezoid where another pair of right-eye and left-eye pixels is treatedas the lower base and a light-blocking portions in a parallax barriertherefor as the upper base falls toward the viewer and is furtherdistorted as the trapezoid is more distant from the pixels that face thefront of the viewer in the horizontal direction, and so that theparallax barrier prevents the left eye of the viewer from seeing thepixel region for the right eye and the right eye of the viewer fromseeing the pixel region for the left eye. Note that the sixth step maybe performed at the same time as the fifth step.

<Method for Specifying Position of Viewer With Respect to Pixels>

In this embodiment, the position of the viewer is specified by theviewer detection circuit 160 connected to the ultrasonic generator 161provided between the two detectors 162R and 162L. Specifically, a pulsedultrasonic wave is transmitted to a space facing the display surface ofthe display device by using the ultrasonic generator 161. When theviewer is present in the space, the pulsed ultrasonic wave is reflectedand the reflected wave is detected by the detectors 162R and 162L. Onthe other hand, when the viewer is absent in the space, the pulsedultrasonic wave passes through the space without a reflected wavereturned.

The viewer detection circuit 160 measures a time after a pulsedultrasonic wave is emitted from the ultrasonic generator 161 until thereflected wave is detected by the detectors 162R and 162L, to detectwhether an object is present in the space. When the object is present inthe space, the distance between the object and the detector 162R and thedistance between the object and the detector 162L can be found.Moreover, object location information can be obtained from the intensityof the reflected wave.

The detectors 162R and 162L are fixed at given positions with respect tothe display panel. For example, as illustrated in FIG. 1A, the detector162R is fixed at the right edge of the display panel and the detector162L is fixed at the left edge. Further, the pixels are fixed at givenpositions in the display panel. Accordingly, the position of the viewerwith respect to the pixels can be specified by detecting the position ofthe viewer using a plurality of detectors fixed at given positions withrespect to the display panel.

Note that the number of ultrasonic generators may be one or more, and aplurality of generators can be used. In addition, a plurality ofdetectors can be used, that is, the number of detectors is not limitedto two. The increase in the number of detectors provided apart from eachother enhances the accuracy of specifying the position of the viewer.The ultrasonic generator is not necessarily provided between detectorsas long as an ultrasonic wave emitted from the ultrasonic generator isreflected by the viewer and the reflected wave is received by thedetectors.

<Mode of Parallax Barrier According to Position of Viewer>

Next, a description is given of a mode of a parallax barrier accordingto the position of the viewer specified by the viewer detection circuit160.

FIGS. 2A and 2B schematically illustrate the relation between a mode ofa parallax barrier and the distance between a viewer and a displaypanel. FIG. 2A schematically illustrates the viewpoint of the viewer andcross sections of a display panel 200 and a parallax barrier 90, whichare cut along a plane passing through the right and left eyes of theviewer. In the parallax barrier, light-transmitting regions andlight-blocking regions are alternately provided. The mode of theparallax barrier can be a stripe pattern, a checkered pattern, a crossedpattern (oblique pattern), or the like. Note that FIG. 2A shows thecross section of the stripe-shaped parallax barrier. The area of thedisplay panel seen through the gaps in the parallax barrier is extendedas the viewer 10 gets closer to the display panel 200. Specifically, theleft eye sees part of the second pixel region adjacent to the firstpixel region, and the right eye sees part of the first pixel regionadjacent to the second pixel region. As a result, the viewer sees partof an image for the right eye, which is not supposed to be seen with theleft eye, and sees part of an image for the left eye, which is notsupposed to be seen with the right eye; therefore, it becomes difficultfor the viewer to perceive 3D images.

In view of the above, in one embodiment of the present invention, themode of the parallax barrier is changed in accordance with the positionof the viewer. Specifically, the widths of light-blocking portions inthe stripe-shaped parallax barrier are increased to narrow the spacebetween the light-blocking portions. For example, as illustrated in FIG.2B, the widths of light-blocking portions in the parallax barrier 90 areincreased in response to the viewer 10 whose distance to the displaypanel 200 is smaller than that in FIG. 2A, to reduce the widths oflight-transmitting portions. By employing such a structure to controlthe mode of the parallax barrier, the left eye can see only the firstpixel regions and the right eye can see only the second pixel regionseven when the viewer comes close to the display panel.

Next, the case where the viewer 10 moves along the display panel fromthe center portion will be described with reference to FIGS. 3A and 3B,focusing on a trapezoid where a pair of right-eye and left-eye pixels istreated as the lower base and a light-blocking portions in a parallaxbarrier therefor as the upper base

In the mode of the parallax barrier 90 that is optimized while theviewer 10 faces the center portion of the display panel (see FIG. 3A),the trapezoid falls toward the center portion of the display panel 200and is distorted; consequently, it becomes difficult for the viewer toperceive 3D images when the viewer moves along the display panel.

In view of the above, in one embodiment of the present invention, themode of the parallax barrier is changed in accordance with the positionof the viewer. Specifically, the parallax barrier (e.g., thestripe-shaped light-blocking portion) is formed so that its center isaligned with the boundary between a pixel for the right eye and a pixelfor the left eye adjacent to each other at the front of the viewer. Forexample, as illustrated in FIG. 3B, the parallax barrier 90 is formed sothat the trapezoid in which a pixel for the left eye included in thefirst pixel region 210 for the left eye 10L and a pixel for the righteye included in the second pixel region 220 for the right eye 1OR aretreated as the lower base and the light-blocking portions in theparallax barrier 90 therefor as the upper base is symmetrical at thefront of the viewer 10.

With such a structure, only the first pixel regions 210 can be seen withthe left eye and only the second pixel regions 220 can be seen with theright eye at the front of the viewer 10.

As for a parallax barrier positioned on the right side or left side ofthe viewer, a stripe-shaped parallax barrier is formed so that thetrapezoid falls toward the front side of the viewer and is furtherdistorted as the trapezoid is more distant from the front of the viewer.This is because the viewer positions themselves to see the display panelfrom an oblique direction; therefore, if a parallax barrier is formed sothat its center can be aligned with the boundary between the pixel forthe right eye and the pixel for the left eye, the left eye sees aright-eye image and the right eye sees a left-eye image. For thatreason, when focusing on a trapezoid in which a pair of right-eye andleft-eye pixels is treated as the lower base and a light-blockingportions in a parallax barrier therefor as the upper base, a parallaxbarrier needs to be formed by controlling the width and space betweenlight-blocking portions in the stripe-shaped parallax barrier so thatthe trapezoid falls toward the front side of the viewer and itsdistortion increases as the trapezoid is more distant from the front ofthe viewer.

With such a structure, the left eye can see only the first pixel regions210 and the right eye can see only the second pixel regions 220 from adirection away from the front of the viewer.

In the display device according to one embodiment of the presentinvention, the mode of a parallax barrier is changed in accordance withthe position of a viewer specified by a plurality of detectors and anultrasonic generator with respect to pixels. Thus, the position of theright eye and left eye of the specified viewer with respect to each ofthe pixels included in the display device can be found. Consequently, itis possible to provide a display device with an extended area where thespecified viewer can perceive 3D images with the naked eye. Further,since an ultrasonic wave is used, the position of the viewer can beaccurately detected even in a dark environment. As a result, the viewercan perceive brighter and clearer 3D display images.

This embodiment can be freely combined with any of the other embodimentsin this specification as appropriate.

Embodiment 2

In this embodiment, a shutter panel applicable to a display device inwhich a mode of a parallax barrier is changed in accordance with theposition of a viewer with respect to pixels will be described withreference to FIGS. 4A, 4A2, 4B1, and 4B2 and FIG. 5. Specifically, adescription is given of the structure of a shutter panel in which aliquid crystal layer is sandwiched between a pair of substrates, atleast one of the pair of substrates is provided with a plurality ofelectrodes for controlling alignment of liquid crystals in the liquidcrystal layer, and each of the plurality of electrodes is electricallyconnected to a parallax barrier control circuit.

In the shutter panel, a parallax barrier with a variety of modes isformed. Specifically, the shutter panel is constituted by a plurality ofoptical elements whose state is switched between a light-blocking stateand a light-transmitting state. As the optical element whose state isswitched between a light-blocking state and a light-transmitting state,it is preferable to use a liquid crystal element in which liquidcrystals are placed between a pair of electrodes. The state (alight-blocking state or a light-transmitting state) of the liquidcrystal element can be selectively controlled by controlling alignmentof the liquid crystals by application of an electric field to the liquidcrystal layer sandwiched between the pair of electrodes.

<Structure of Shutter Panel>

FIG. 4A1 is a top view of the shutter panel 100. FIG. 4A2 is across-sectional view along Y1-Y2 in FIG. 4A1.

The shutter panel 100 includes electrodes 106 on a substrate 101 andelectrodes 105 on a substrate 102. The electrodes 106 include aplurality of stripe-shaped electrodes (106 a 1, 106 a 2, 106 a 3, 106 b1, 106 b 2, 106 b 3, 106 c 1, 106 c 2, and 106 c 3). The electrodes 105include a plurality of stripe-shaped electrodes (105 a 1, 105 a 2, 105 a3, 105 b 1, 105 b 2, 105 b 3, 105 c 1, 105 c 2, and 105 c 3). In thisembodiment, the electrodes are electrically independent of each otherand can be controlled by the parallax barrier control circuit.

In the shutter panel 100, a liquid crystal layer 103 is sandwichedbetween the substrate 101 and the substrate 102 that overlap with eachother so that the electrodes 106 intersect the electrodes 105. Liquidcrystal elements are formed at positions where the stripe-shapedelectrodes included in the electrodes 106 intersect the stripe-shapedelectrodes included in the electrodes 105, and thus are arranged in adotted pattern.

Switching between a light-blocking state and a light-transmitting stateof the liquid crystal element can be accomplished by application ofvoltage to the pair of stripe-shaped electrodes included in the liquidcrystal element.

Specifically, as illustrated in FIG. 4A2, liquid crystal elements 107 a1, 107 a 2, and 107 a 3 are formed between the electrode 105 b 1 and theelectrodes 106 a 1, 106 a 2, and 106 a 3. Liquid crystal elements 107 b1, 107 b 2, and 107 b 3 are formed between the electrode 105 b 1 and theelectrodes 106 b 1, 106 b 2, and 106 b 3. Liquid crystal elements 107 c1, 107 c 2, and 107 c 3 are formed between the electrode 105 b 1 and theelectrodes 106 c 1, 106 c 2, and 106 c 3.

A plurality of such optical elements whose state is switched between alight-blocking state and a light-transmitting state are arranged in amatrix, thereby forming a parallax barrier in which a light-blockingregion and a light-transmitting region can be minutely controlled. Notethat it is possible that the electrodes 105 a to 105 c and theelectrodes 106 a to 106 c are divided into more than two electrodes, andthat the divided electrodes have different line widths.

FIG. 4B1 is a top view of another structure of the electrode 106 bapplicable to the shutter panel 100. FIG. 4B2 is a cross-sectional viewalong Y3-Y4 of the electrode 106 b in the shutter panel in which theelectrodes 105 overlap the electrode 106 b so as to intersect theelectrode 106 b and the liquid crystal layer 103 is sandwiched betweenthe substrate 101 and the substrate 102.

As the electrode 106 b illustrated in FIGS. 4B1 and 4B2, a plurality ofelectrodes with a narrow line width (106 b 1, 106 b 2, 106 b 3, 106 b 5,106 b 6, and 106 b 7) are provided on the both sides of an electrode 106b 4. In this manner, the electrodes 106 and the electrodes 105 do notnecessarily have the same width.

<Method for Driving Shutter Panel>

A method for driving the shutter panel including the electrode 106 billustrated in FIGS. 4B1 and 4B2 will be described.

When a viewer is relatively far from the display panel, the parallaxbarrier control circuit selects the electrode 106 b 4 to form a parallaxbarrier. When the viewer comes closer to the display panel, the parallaxbarrier control circuit additionally selects the electrodes 106 b 3 and106 b 5 adjacent to the electrode 106 b 4 and drives the shutter panelso that a light-blocking region of the parallax barrier is extended. Bydriving the shutter panel 100 in such a manner, the left eye can seeonly the pixel regions for the left eye and the right eye can see onlythe pixel regions for the right eye even when the viewer is close to thedisplay panel. As a result, the area where the viewer can perceive 3Dimages is extended.

The parallax barrier control circuit selects the electrode 106 b 4 whenthe viewer is positioned at the front of the electrode 106 b 4, andselects the electrode 106 b 5 in addition to the electrode 106 b 4 whenthe viewer is positioned on the right side (from our view) of the frontof the electrode 106 b 4 so that a light-blocking region of the parallaxbarrier is extended to the viewer side. By driving the shutter panel 100in such a manner, the left eye can see only the pixel regions for theleft eye and the right eye can see only the pixel regions for the righteye even when the viewer is close to the display panel. Consequently,the area where the viewer can perceive 3D images is extended.

<Another Structure of Shutter Panel>

In addition, an element that functions as a switch electricallyconnected to a liquid crystal element can be provided to control theliquid crystal element. FIG. 5 illustrates an example of a shutter panelin which a transistor is provided as an element functioning as a switchto drive a liquid crystal element.

The shutter panel in FIG. 5 includes a first liquid crystal elementhaving an electrode 116 a 1 electrically connected to a transistor 120 a1, a second liquid crystal element that is adjacent to the first liquidcrystal element and has an electrode 116 a 2 electrically connected to atransistor 120 a 2, a third liquid crystal element having an electrode116 a 3 electrically connected to a transistor 120 a 3, and a capacitorwiring 124.

Although not illustrated, electrodes paired with the electrodes 116 a 1to 116 a 3 are provided over the electrodes 116 a 1 to 116 a 3 withliquid crystals placed therebetween.

The transistors 120 a 1, 120 a 2, and 120 a 3 electrically connected toa wiring 121 a are electrically connected to a wiring 122 a 1, a wiring122 a 2, and a wiring 122 a 3, respectively.

FIG. 5 shows an example in which the sizes (areas) of the electrodes 116a 1, 116 a 2, and 116 a 3 are almost the same; however, there is noparticular limitation on the sizes, and the electrodes 116 a 1 to 116 a3 may have different sizes. Further, a larger number of (three or more)liquid crystal elements may be provided on the both sides of the liquidcrystal element having the electrode 116 a.

When 3D images are to be displayed, the light-blocking region can beselectively determined by controlling the first, second, and thirdliquid crystal elements. For example, a first light-blocking regionformed by driving only the first liquid crystal element, a secondlight-blocking region formed by driving the first and second liquidcrystal elements, and a third light-blocking region formed by drivingthe first, second, and third liquid crystal elements can be formed.

By driving the shutter panel 100 in such a manner, the left eye can seeonly the pixel regions for the left eye and the right eye can see onlythe pixel regions for the right eye even when the viewer is close to thedisplay panel. As a result, the area where the viewer can perceive 3Dimages is extended.

Although not shown in this embodiment, the shutter panel is providedwith an optical film such as a polarizing plate, a retardation plate, oran anti-reflection film, or the like as appropriate. For the shutterpanel, a transmissive liquid crystal element with a variety ofstructures and a variety of liquid crystal modes can be employed.

For example, with the structure where liquid crystals are sandwichedbetween a pair of electrodes like the structures illustrated in FIGS.4A1 to 4B2, the gray level can be controlled by generating an electricfield substantially vertical to the substrate to move liquid crystalmolecules in a plane vertical to the substrate. Further, the electrodesof the liquid crystal element in FIG. 5 can have a structure for an IPSor FFS mode, in which case the gray level can be controlled bygenerating an electric field substantially parallel (horizontal) to thesubstrate to move liquid crystal molecules in a plane parallel to thesubstrate.

There is no particular limitation on the structure of the transistorused in the shutter panel; for example, a staggered transistor or aplanar transistor having a top-gate structure or a bottom-gate structurecan be used. The transistor may have a single-gate structure in whichone channel formation region is formed, a double-gate structure in whichtwo channel formation regions are formed, or a triple-gate structure inwhich three channel formation regions are formed. Alternatively, thetransistor may have a dual-gate structure including two gate electrodelayers positioned over and below a channel formation region with a gateinsulating layer provided therebetween.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

Embodiment 3

In this embodiment, examples of the structure of a display panelapplicable to the display panel in Embodiment 1 will be described withreference to FIGS. 6A and 6B and FIGS. 7A and 7B.

As a display element provided in the display panel, a light-emittingelement (also referred to as a light-emitting display element) or aliquid crystal element (also referred to as a liquid crystal displayelement) can be used. A light-emitting element includes, in itscategory, an element whose luminance is controlled by current orvoltage, and specifically includes an inorganic electroluminescent (EL)element, an organic EL element, and the like.

FIGS. 6A and 6B illustrate an example of the structure of a displaypanel in which an organic EL element is used as a display element. FIG.6A is a plan view of the display panel. FIG. 6B is a cross-sectionalview along A-B and C-D in FIG. 6A. An element substrate 410 is fixed toa sealing substrate 404 with a sealant 405, and includes driver circuitunits (a source driver circuit 401 and a gate driver circuit 403) and apixel portion 402 including a plurality of pixels.

A wiring 408 is a wiring for transmitting signals input to the sourcedriver circuit 401 and the gate driver circuit 403, and receives a videosignal, a clock signal, a start signal, a reset signal, and the likefrom a flexible printed circuit (FPC) 409 serving as an external inputterminal Although only the FPC is illustrated here, a printed wiringboard (PWB) may be attached to the FPC. The display panel in thisspecification includes not only a main body of the display panel but onewith an FPC or a PWB attached thereto.

The driver circuit units (the source driver circuit 401 and the gatedriver circuit 403) and the pixel portion 402 are formed over theelement substrate 410. FIG. 6B illustrates the source driver circuit401, which is the driver circuit unit, and three pixels in the pixelportion 402.

This embodiment explains an example in which the pixel portion 402includes pixels of three colors: a blue (B) pixel 420 a, a green (G)pixel 420 b, and a red (R) pixel 420 c. Note that this embodiment is notlimited to this example, and a display panel can display multi-colorimages by including pixels of at least two colors in the pixel portion402, or alternatively may be a display panel for single color display.

Pixels 420 a, 420 b, and 420 c respectively include color filter layers434 a, 434 b, and 434 c; light-emitting elements 418 a, 418 b, and 418c; and transistors 412 a, 412 b, and 412 c that are electricallyconnected to the light-emitting elements 418 a, 418 b, and 418 c andfunction as switching transistors. Moreover, a black matrix 435 thatsurrounds the color filter layers 434 a, 434 b, and 434 c is formed.

The color filter layer can be provided to correspond to the color ofeach pixel. For example, the color filter layer 434 a of the blue (B)pixel 420 a is blue; the color filter layer 434 b of the green (G) pixel420 b is green; and the color filter layer 434 c of the red (R) pixel420 c is red.

The light-emitting elements 418 a, 418 b, and 418 c include respectivereflective electrodes 413 a, 413 b, and 413 c, an EL layer 431, and alight-transmitting electrode 433. Each of the reflective electrodes 413a, 413 b, and 413 c is used as one of an anode and a cathode, and thelight-transmitting electrode 433 is used as the other of the anode andthe cathode.

The EL layer 431 has at least a light-emitting layer. The EL layer 431can have a stacked structure including a hole-injection layer, ahole-transport layer, an electron-transport layer, an electron-injectionlayer, and/or the like in addition to the light-emitting layer. Inaddition, a plurality of EL layers may be stacked, and a chargegeneration layer may be provided between one EL layer and another ELlayer. When a plurality of light-emitting layers are stacked between theanode and the cathode, the light-emitting element can emit white light,for example.

Light-transmitting conductive layers 415 a, 415 b, and 415 c may beprovided between the respective reflective electrodes 413 a, 413 b, and413 c and the EL layer 431. The light-transmitting conductive layers 415a, 415 b, and 415 c have a function of adjusting the optical distancebetween the reflective electrodes 413 a, 413 b, and 413 c and thelight-transmitting electrode 433 in each pixel. By enhancing a desiredspectrum with a microcavity for each light-emitting element, a displaypanel with high color purity can be provided.

FIG. 6B shows the top-emission display panel that includes a combinationof light-emitting elements emitting white light and color filters; thedisplay panel can be a top-emission display panel includinglight-emitting elements formed by a separate coloring method. A separatecoloring method is a method by which materials for RGB are applied torespective pixels by evaporation or the like.

When the light-emitting layer is formed as a continuous film instead ofbeing separately formed for every pixel using a metal mask, a reductionin yield and complication of the process due to the use of the metalmask can be avoided. Consequently, a high definition display panel withhigh color reproducibility can be achieved.

As the source driver circuit 401, a CMOS circuit including a combinationof an n-channel transistor 423 and a p-channel transistor 424 is formed.The gate driver circuit 403 may be constituted by a variety of circuitsformed with transistors, such as a CMOS circuit, a PMOS circuit, or anNMOS circuit. This embodiment explains the example in which the sourcedriver circuit and the gate driver circuit are formed over thesubstrate; however, the structure is not necessarily limited thereto,and part or all of the source driver circuit and the gate driver circuitcan be formed on the periphery of the substrate instead of over thesubstrate.

An insulator 414 is formed to cover end portions of the reflectiveelectrodes 413 a, 413 b, and 413 c and the light-transmitting conductivelayers 415 a, 415 b, and 415 c. Here, the insulator 414 is formed usinga positive type photosensitive acrylic resin film.

In order to improve the coverage, the insulator 414 is provided suchthat either an upper end portion or a lower end portion of the insulator414 has a curved surface with a curvature. For example, when positivetype photosensitive acrylic is used as a material for the insulator 414,it is preferable that only the upper end portion of the insulator 414have a curved surface with a curvature radius (0.2 μm to 3 μm). Theinsulator 414 can be formed using either a negative type which becomesinsoluble in an etchant by light irradiation or a positive type whichbecomes soluble in an etchant by light irradiation.

The sealing substrate 404 is attached to the element substrate 410 withthe sealant 405; thus, the light-emitting elements 418 a, 418 b, and 418c are provided in a space 407 enclosed by the element substrate 410, thesealing substrate 404, and the sealant 405. The space 407 is filled witha filler such as an inert gas (e.g., nitrogen or argon), an organicresin, or the sealant 405. As the organic resin and the sealant 405,materials containing a hygroscopic substance may be used.

Note that as the sealant 405, an epoxy-based resin is preferably used.It is preferable that such a material do not transmit moisture or oxygenas much as possible. As the sealing substrate 404, a glass substrate, aquartz substrate, or a plastic substrate of fiberglass-reinforcedplastics (FRP), polyvinyl fluoride (PVF), polyester, acrylic, or thelike can be used.

As in this embodiment, an insulating film 411 serving as a base film maybe provided between the element substrate 410 and a semiconductor layerof the transistor. The insulating film has a function of preventingdiffusion of an impurity element from the element substrate 410, and canbe formed with a single-layer structure or a stacked structure using oneor more of a silicon nitride film, a silicon oxide film, a siliconnitride oxide film, and a silicon oxynitride film.

In this embodiment, there is no particular limitation on the structureof the transistor applicable to the display panel; for example, astaggered transistor or a planar transistor having a top-gate structureor a bottom-gate structure can be used. The transistor may have asingle-gate structure in which one channel formation region is formed, adouble-gate structure in which two channel formation regions are formed,or a triple-gate structure in which three channel formation regions areformed. Alternatively, the transistor may have a dual-gate structureincluding two gate electrode layers positioned over and below a channelformation region with a gate insulating layer provided therebetween.

The gate electrode layer can be formed with a single-layer structure ora layered structure using a metal material such as molybdenum, titanium,chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium,or an alloy or a compound that contains any of these materials as itsmain component.

For example, as a two-layer structure of the gate electrode layer, thefollowing structures are preferable: a two-layer structure of analuminum layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a molybdenum layer stacked thereover, atwo-layer structure of a copper layer and a titanium nitride layer or atantalum nitride layer stacked thereover, and a two-layer structure of atitanium nitride layer and a molybdenum layer. As a three-layerstructure, it is preferable to employ a stacked structure in which atungsten layer or a tungsten nitride layer, an aluminum-silicon alloylayer or an alloy layer of aluminum and titanium, and a titanium nitridelayer or a titanium layer are stacked.

The gate insulating layer can be formed with a single-layer structure ora stacked structure of a silicon oxide layer, a silicon nitride layer, asilicon oxynitride layer, and/or a silicon nitride oxide layer by plasmaCVD, sputtering, or the like.

Alternatively, a silicon oxide layer formed by CVD using an organosilanegas can be used as the gate insulating layer. As an organosilane gas, asilicon-containing compound such as tetraethoxysilane (TEOS:Si(OC₂H₅)₄), tetramethylsilane (TMS: Si(CH₃)₄),tetramethylcyclotetrasiloxane (TMCTS), octamethylcyclotetrasiloxane(OMCTS), hexamethyldisilazane (HMDS), triethoxysilane (SiH(OC₂H₅)₃), ortris(dimethylamino)silane (SiH(N(CH₃)₂)₃) can be used.

A material of the semiconductor layer is not limited to a particularmaterial and determined in accordance with characteristics needed forthe transistors 412 a, 412 b, 412 c, 423, and 424 as appropriate.Examples of a material that can be used for the semiconductor layer willbe described.

The semiconductor layer can be formed using the following material: anamorphous semiconductor manufactured by sputtering or by vapor-phasegrowth using a semiconductor material gas typified by silane or germane;a polycrystalline semiconductor formed by crystallizing the amorphoussemiconductor with the use of light energy or thermal energy; amicrocrystalline semiconductor; or the like. The semiconductor layer canbe deposited by sputtering, LPCVD, plasma CVD, or the like.

For the semiconductor layer, a single crystal semiconductor (e.g.,single crystal silicon or single crystal silicon carbide) can be used.When a single crystal semiconductor is used for the semiconductor layer,the size of the transistor can be reduced, leading to a higher densityof pixels in a display portion. When a single crystal semiconductor isused for the semiconductor layer, an SOI substrate including a singlecrystal semiconductor layer can be used. Alternatively, a semiconductorsubstrate such as a silicon wafer may be used.

A typical example of an amorphous semiconductor is hydrogenatedamorphous silicon, and a typical example of a crystalline semiconductoris polysilicon. Examples of polysilicon (polycrystalline silicon) arehigh-temperature polysilicon that contains polysilicon formed at aprocess temperature of 800° C. or higher as its main component,low-temperature polysilicon that contains polysilicon formed at aprocess temperature of 600° C. or lower as its main component, andpolysilicon obtained by crystallizing amorphous silicon using an elementthat promotes crystallization or the like. Needless to say, amicrocrystalline semiconductor or a semiconductor that includes acrystalline phase in part of a semiconductor layer can be used asdescribed above.

Further, an oxide semiconductor may be used. Examples of an oxidesemiconductor are an In—Sn—Ga—Zn—O-based oxide semiconductor which is anoxide of four metal elements; an In—Ga—Zn—O-based oxide semiconductor,an In—Sn—Zn—O-based oxide semiconductor, an In—Al—Zn—O-based oxidesemiconductor, a Sn—Ga—Zn—O-based oxide semiconductor, anAl—Ga—Zn—O-based oxide semiconductor, and a Sn—Al—Zn—O-based oxidesemiconductor which are oxides of three metal elements; an In—Zn—O-basedoxide semiconductor, a Sn—Zn—O-based oxide semiconductor, anAl—Zn—O-based oxide semiconductor, a Zn—Mg—O-based oxide semiconductor,a Sn—Mg—O-based oxide semiconductor, an In—Mg—O-based oxidesemiconductor, and In—Ga—O-based oxide semiconductor which are oxides oftwo metal elements; and an In—O-based oxide semiconductor, a Sn—O-basedoxide semiconductor, and a Zn—O-based oxide semiconductor which areoxides of one metal element. Moreover, SiO₂ may be contained in theabove oxide semiconductor. Here, for example, the In—Ga—Zn—O-based oxidesemiconductor means an oxide containing at least In, Ga, and Zn, andthere is no particular limitation on the composition ratio of theelements. The In—Ga—Zn—O-based oxide semiconductor may contain anelement other than In, Ga, and Zn.

For the oxide semiconductor layer, a thin film expressed by a chemicalformula of InMO₃(ZnO)_(m) (m>0) can be used. Here, M represents one ormore metal elements selected from Ga, Al, Mn, and Co. For example, M canbe Ga, Ga and Al, Ga and Mn, or Ga and Co.

In the case where an In—Zn—O-based material is used as the oxidesemiconductor, the atomic ratio is In/Zn=0.5 to 50, preferably In/Zn=1to 20, further preferably In/Zn=1.5 to 15. When the atomic ratio of Into Zn is in the above preferred range, the field-effect mobility of thetransistor can be improved. Here, when the atomic ratio of the compoundis In:Zn:O=X:Y:Z, the relation Z>1.5X+Y is satisfied.

For the oxide semiconductor layer, it is possible to use an oxidesemiconductor that has neither a single crystal structure nor anamorphous structure and is a crystalline oxide semiconductor havingc-axis alignment (also referred to as a c-axis aligned crystalline oxidesemiconductor (CAAC-OS)).

Examples of a material of wiring layers serving as source and drainelectrode layers are an element selected from Al, Cr, Ta, Ti, Mo, and W;an alloy or a compound containing any of the above elements as itscomponent; and an alloy or a compound containing a combination of any ofthese elements. Further, in the case where heat treatment is performed,the conductive film preferably has heat resistance against the heattreatment. Since the use of aluminum alone brings disadvantages such aslow heat resistance and a tendency to corrosion, aluminum is used incombination with a conductive material having heat resistance. As theconductive material having heat resistance, which is used in combinationwith aluminum, it is possible to use an element selected from titanium(Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr),neodymium (Nd), and scandium (Sc), an alloy containing any of theseelements as its component, an alloy containing a combination of any ofthese elements, or a nitride containing any of these elements as itscomponent.

As an insulating film 419 that covers the transistor, an inorganicinsulating film or an organic insulating film formed by a dry method ora wet method can be used. For example, it is possible to use a siliconnitride film, a silicon oxide film, a silicon oxynitride film, analuminum oxide film, a tantalum oxide film, or a gallium oxide filmformed by CVD, sputtering, or the like. Moreover, an organic materialsuch as polyimide, acrylic, benzocyclobutene, polyamide, or an epoxyresin can be used. Other than such organic materials, it is alsopossible to use a low-dielectric constant material (a low-k material), asiloxane-based resin, PSG (phosphosilicate glass), BPSG(borophosphosilicate glass), or the like.

Note that a siloxane-based resin corresponds to a resin including aSi—O—Si bond formed using a siloxane-based material as a startingmaterial. A siloxane-based resin may include an organic group (e.g., analkyl group or an aryl group) or a fluoro group as a substituent. Inaddition, the organic group may include a fluoro group. A siloxane-basedresin is applied by a coating method and baked; thus, the insulatingfilm 419 can be formed.

Note that the insulating film 419 may be formed by stacking a pluralityof insulating films each formed using any of the above materials. Forexample, the insulating film 419 may have a structure in which anorganic resin film is stacked over an inorganic insulating film.

FIGS. 7A and 7B illustrate an example of a display panel including aliquid crystal element as a display element. FIG. 7A is a plan view of adisplay panel, and FIG. 7B is a cross-sectional view along E-F in FIG.7A. The structure of the panel including the liquid crystal elementshown in this embodiment can be employed as the structure of the shutterpanel as appropriate.

In FIG. 7B, a sealant 605 is provided so as to surround a pixel portion602 and a scan line driver circuit 604 which are provided over a firstsubstrate 601. A second substrate 606 is provided over the pixel portion602 and the scan line driver circuit 604. Thus, the pixel portion 602and the scan line driver circuit 604 are sealed together with thedisplay element by the first substrate 601, the sealant 605, and thesecond substrate 606.

In FIG. 7A, a signal line driver circuit 603 that is formed using asingle crystal semiconductor film or a polycrystalline semiconductorfilm over a substrate separately prepared is mounted in a regiondifferent from the region surrounded by the sealant 605 over the firstsubstrate 601. A variety of signals and potentials are supplied to thesignal line driver circuit 603, the scan line driver circuit 604, andthe pixel portion 602 from an FPC 618.

In FIGS. 7A and 7B, the display panel includes a connection terminalelectrode 615 and a terminal electrode 616. The connection terminalelectrode 615 and the terminal electrode 616 are electrically connectedto a terminal of the FPC 618 via an anisotropic conductive film 619. Theconnection terminal electrode 615 is formed using the same conductivefilm as a first electrode layer 630 of the liquid crystal element, andthe terminal electrode 616 is formed using the same conductive film assource and drain electrodes of transistors 610 and 611.

The pixel portion 602 and the scan line driver circuit 604, which areprovided over the first substrate 601, each include a plurality oftransistors. FIG. 7B illustrates the transistor 610 included in thepixel portion 602 and the transistor 611 included in the scan linedriver circuit 604.

In FIG. 7B, a liquid crystal element 613, which is the display element,includes the first electrode layer 630, a second electrode layer 631,and the liquid crystal layer 608. Insulating films 632 and 633 servingas alignment films are provided so that the liquid crystal layer 608 issandwiched therebetween. The second electrode layer 631 is provided onthe second substrate 606 side, and the first electrode layer 630 and thesecond electrode layer 631 are stacked with the liquid crystal layer 608placed therebetween.

A columnar spacer 635 is obtained by selective etching of an insulatingfilm. The spacer is provided to control the thickness (cell gap) of theliquid crystal layer 608. Alternatively, a spherical spacer may be used.

In the case where a liquid crystal element is used as the displayelement, thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal,ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. These liquid crystal materials exhibit a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on conditions.

Alternatively, liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. A blue phase is one of liquidcrystal phases, which is generated just before a cholesteric phasechanges into an isotropic phase while temperature of cholesteric liquidcrystal is increased. Since the blue phase appears only in a narrowtemperature range, a liquid crystal composition in which several weightpercent or more of a chiral material is mixed is used for the liquidcrystal layer in order to extend the temperature range. The liquidcrystal composition that includes a liquid crystal showing a blue phaseand a chiral agent has a short response time of 1 ms (millisecond) orless and has optical isotropy; therefore, the alignment process is notnecessary and viewing angle dependence is small. In addition, since analignment film does not need to be provided and rubbing treatment isunnecessary, electrostatic discharge caused by the rubbing treatment canbe prevented and defects and damage of the display panel can be reducedin the manufacturing process. Thus, the productivity of the displaypanel can be increased.

The specific resistivity of the liquid crystal material is 1×10⁹ Ω·cm ormore, preferably 1×10¹¹ Ω·m or more, further preferably 1×10¹² Ω·cm ormore. The value of the specific resistivity in this specification ismeasured at 20° C.

For the display panel including the liquid crystal elements (the liquidcrystal display panel), a twisted nematic (TN) mode, anin-plane-switching (IPS) mode, a fringe field switching (FFS) mode, anaxially symmetric aligned micro-cell (ASM) mode, an opticallycompensated birefringence (OCB) mode, a ferroelectric liquid crystal(FLC) mode, an antiferroelectric liquid crystal (AFLC) mode, or the likecan be used.

The display panel in this embodiment can be a normally black liquidcrystal display panel such as a transmissive liquid crystal displaypanel utilizing a vertical alignment (VA) mode. The vertical alignmentmode is a method of controlling alignment of liquid crystal molecules ofa liquid crystal display panel, in which liquid crystal molecules arealigned orthogonally to a panel surface when no voltage is applied.There are some examples of the vertical alignment mode, and forinstance, a multi-domain vertical alignment (MVA) mode, a patternedvertical alignment (PVA) mode, or an advanced super view (ASV) mode canbe employed. Moreover, it is possible to use a method called domainmultiplication or multi-domain design, in which a pixel is divided intoseveral regions (subpixels) and molecules are aligned in differentdirections in their respective regions.

In the display panel described in this embodiment, a black matrix (alight-shielding layer), an optical member (an optical substrate) such asa polarizing member, a retardation member, or an anti-reflection member,and the like are provided as appropriate. For example, circularpolarization may be obtained by using a polarizing substrate and aretardation substrate. In addition, a backlight, a side light, or thelike may be used as a light source for the liquid crystal display panel.

As a display method in the pixel portion, a progressive method, aninterlace method, or the like can be employed. Further, color elementscontrolled in a pixel at the time of color display are not limited tothree colors: R, G, and B (R, G, and B correspond to red, green, andblue). For example, R, G, B, and W (W corresponds to white); or R, G, B,and one or more of yellow, cyan, magenta, and the like can be used. Notethat the size of display regions may be different between dots of colorelements. This embodiment is not limited to the application to a displaypanel for color display but can also be applied to a display panel formonochrome display.

The display device according to one embodiment of the present inventioncan be provided by applying the display panel described in thisembodiment to the display panel in Embodiment 1.

Note that this embodiment can be implemented in appropriate combinationwith the structures described in the other embodiments.

Embodiment 4

The display device according to one embodiment of the present inventionmay include a position input device called a touch panel. In thisembodiment, a description is given using FIGS. 8A and 8B of an exampleof the structure of a shutter panel that is applicable to the displaydevice in one embodiment of the present invention and includes a touchpanel.

FIG. 8A is a perspective view of a shutter panel shown in thisembodiment. FIG. 8B is a cross-sectional view along M-N in FIG. 8A. Notethat in FIG. 8A, some of components (e.g., a polarizing plate) areomitted in order to avoid complexity of the drawing.

A shutter panel 640 illustrated in FIGS. 8A and 8B includes a firstpolarizing plate 642, a liquid crystal element unit 650, a touch panelunit 660 provided to overlap with the liquid crystal element unit 650, asecond polarizing plate 648, and a substrate 652 provided in contactwith the second polarizing plate 648.

The liquid crystal element unit 650 includes a plurality of liquidcrystal elements provided between a substrate 644 and a substrate 646.The plurality of liquid crystal elements can have the structure shown inEmbodiment 2.

An arrow in FIG. 8B indicates the direction of emitted light, whichmeans that a display panel is provided on the first polarizing plate 642side in the display device according to one embodiment of the presentinvention.

For the touch panel unit 660, the capacitive touch technology can beused, for example. FIGS. 8A and 8B show an example of the structureusing a projected capacitive touch technology. The touch panel unit 660includes a plurality of first electrodes 662, an insulating layer 666covering the first electrodes 662, a plurality of second electrodes 664,and an insulating layer 668 covering the second electrodes 664.

The first electrode 662 has a structure where a plurality of rectangularconductive films 661 are connected to each other. The second electrode664 has a structure where a plurality of rectangular conductive films663 are connected to each other. The plurality of the first electrodes662 and the plurality of the second electrodes 664 overlap with eachother so that the positions of the rectangular conductive films 661 aredifferent from those of the rectangular conductive films 663. Note thatthe shapes of the first electrodes 662 and the second electrodes 664 arenot limited to the above.

The first electrode 662 and the second electrode 664 can be formed usinga light-transmitting conductive material, for example, indium tin oxidecontaining silicon oxide (ITSO), indium tin oxide (ITO), zinc oxide(ZnO), indium zinc oxide, or zinc oxide to which gallium is added (GZO).

One example of the shutter panel including the touch panel unitdescribed in this embodiment has a structure in which the touch panelunit 660 is stacked between the first polarizing plate 642 and thesecond polarizing plate 648 which constitute the shutter panel. Thisstructure can reduce the number of components as compared to the casewhere a shutter panel and a touch panel are manufactured separately andprovided in a display device. As a result, manufacturing costs of thedisplay device can be reduced. Moreover, the weight and thickness of thedisplay device can be reduced.

Note that this embodiment can be implemented in appropriate combinationwith the structures described in the other embodiments.

Embodiment 5

The display device according to one embodiment of the present inventioncan be used for laptops and image reproducing devices provided withrecording media (typically, devices that reproduce the content ofrecording media such as digital versatile discs (DVDs) and have displaysfor displaying the reproduced images). Other examples of electronicdevices that can include the display device according to one embodimentof the present invention are mobile phones, portable game consoles,personal digital assistants, e-book readers, cameras such as videocameras and digital still cameras, goggle-type displays (head mounteddisplays), navigation systems, audio reproducing devices (e.g., caraudio systems and digital audio players), copiers, facsimiles, printers,multifunction printers, automated teller machines (ATM), and vendingmachines. In this embodiment, specific examples of such electronicdevices will be described with reference to FIGS. 9A to 9C.

FIG. 9A illustrates a portable game console including a housing 5001, ahousing 5002, a display portion 5003, a display portion 5004, amicrophone 5005, speakers 5006, operation keys 5007, and a stylus 5008.The display device according to one embodiment of the present inventioncan be used as the display portion 5003 or the display portion 5004. Byusing the display device according to one embodiment of the presentinvention as the display portion 5003 or the display portion 5004, it ispossible to provide a highly convenient portable game console capable ofdisplaying 3D images. Although the portable game console in FIG. 9A hasthe two display portions 5003 and 5004, the number of display portionsincluded in a portable game console is not limited to this.

FIG. 9B illustrates a laptop personal computer including a housing 5201,a display portion 5202, a keyboard 5203, and a pointing device 5204. Thedisplay device according to one embodiment of the present invention canbe used for the display portion 5202. By using the display deviceaccording to one embodiment of the present invention as the displayportion 5202, it is possible to provide a highly convenient laptoppersonal computer capable of displaying 3D images.

FIG. 9C illustrates a personal digital assistant including a housing5401, a display portion 5402, and operation keys 5403. The displaydevice according to one embodiment of the present invention can be usedas the display portion 5402. By using the display device according toone embodiment of the present invention as the display portion 5402, itis possible to provide a highly convenient personal digital assistantcapable of displaying 3D images.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

EXAMPLE

In this example, the structure of a fabricated 3D display device whichis one embodiment of the present invention will be described withreference to FIG. 12. In addition, a method for evaluation andevaluation results of crosstalk observed 30 cm away from the fabricated3D display device will be described with reference to FIGS. 13A-L,13A-R, and 13B and FIG. 14.

<Structure>

FIG. 12 is a block diagram of a fabricated 3D display device 1020. Thefabricated 3D display device 1020 includes a display panel 1200, ashutter panel 1100 in which a parallax barrier is formed, an ultrasonicsensor 1160, and a control device 1030.

The fabricated display panel 1200 is an active matrix organic EL panelprovided with a driver circuit unit (a source driver circuit and a gatedriver circuit) formed over the same substrate. The display panel 1200has a pixel region that is 3.9 inches diagonally. In the pixel region, aplurality of pixels are arranged in a 1440 by 1080 matrix. Each of thepixels has three sub-pixels. The resolution is 458 ppi.

The sub-pixel is 55.5 μm wide and 18.5 μm long. The aperture ratio is60%. Three sub-pixels emit light of red (R), green (G), and blue (B),respectively, and sub-pixels for each color are arranged in a horizontalstripe pattern.

The fabricated shutter panel 1100 is an active matrix shutter panel thatis provided with a driver circuit unit formed over the same substrateand includes a transistor provided for each electrode. The shutter panel1100 has a region where a parallax barrier with a diagonal of 3.9 inchesis formed. In the region, 5760 light-transmitting electrodes with awidth of 11.75 μm are provided in a vertical stripe pattern. Thedistance between two vertical-striped electrodes adjacent to each otheris the smallest (specifically 2 μm) at the center of the region wherethe parallax barrier is formed, and is the largest (specifically 2.25μm) at right and left ends of the region. This is because a viewer islikely to use the 3D display device most frequently when being directlyin front of the center of the device.

The shutter panel 1100 is provided on the display surface side of thedisplay panel 1200 to overlap the display panel 1200. Note that fourvertical-striped electrodes in the shutter panel 1100 overlap one pixelin the display panel 1200.

Further, in the shutter panel 1100, the vertical-striped electrode and acounter electrode between which a nematic liquid crystal layer issandwiched are provided between a pair of polarizing plates. The liquidcrystal element is driven to block incident light, whereby the parallaxbarrier is formed.

The transistor in the shutter panel 1100 includes a crystalline oxidesemiconductor layer having c-axis alignment, specifically anInGaZnO-based oxide semiconductor layer. The transistor has a channelwidth of 50 μm and a channel length of 6 μm, and is of normally offtype. The threshold voltage of the transistor is 1.1 V and the off-statecurrent at 85° C. is 100 yA (10⁻²² A) per channel width of 1 μm.

FIG. 16 shows characteristics of the fabricated transistor afterundergoing the following tests with an illuminance of 10 klx: a test forkeeping the transistor at 80° C. for 1 hour with a gate potential of +20V (+BT test), and a test for keeping the transistor for 1 hour with agate potential of −20 V (−BT test). The right solid line indicates thecharacteristics of the transistor after undergoing the +BT test, and theleft solid line indicates the characteristics of the transistor afterundergoing the −BT test. The dashed line between the two solid linesindicates the characteristics of the transistor before undergoing thesetests.

The shift of the threshold voltage was −0.38 V after the −BT test and+0.8 V after the +BT test.

The ultrasonic sensor 1160 was used to detect the position of theviewer. The ultrasonic sensor 1160 has a time resolution of 20 ms and anangular resolution of 0.5°.

The position of an object is detected in the following manner: theobject reflects an ultrasonic wave emitted from a generator of theultrasonic sensor and detectors of the ultrasonic sensor receive areflected wave. FIGS. 17A to 17C show examples of reflected wavesreceived by the ultrasonic sensor.

FIG. 17A shows an example of the result of detecting a reflected wavewhen the object is placed at a first position, where the object isdirectly in front of the ultrasonic sensor. Right and left detectorsdetected reflected waves with the same amplitude at about the same time.

FIG. 17B shows an example of the result of detecting a reflected wavewhen the object is placed at a second position, where the object iscloser to the right side without changing the distance to the ultrasonicsensor. Although the right and left detectors detected reflected wavesat about the same time, the amplitude of the reflected wave detected bythe right detector was larger than that detected by the left detector.

FIG. 17C shows an example of the result of detecting a reflected wavewhen the object is placed at a third position, at which the object isdirectly in front of the ultrasonic sensor and which is more distantfrom the ultrasonic sensor than the first position. Although the rightand left detectors detected reflected waves with about the sameamplitude, the reflected waves were delayed compared to the case wherethe object was placed at the first position.

A plurality of sensors (Sensor) were arranged in array; each sensorconnected in series with an amplifier (Amp), an analog-to-digitalconverter (ADC), and a delay circuit (Delay) was connected in parallelwith a delay integration circuit (Delay Integration); and delayintegration was performed to detect the position (angle and distance) ofthe object (see FIG. 17D).

<Evaluation Method>

The degree of crosstalk caused 30 cm away from the fabricated 3D displaydevice was evaluated. The method for evaluation will be explained below.

FIGS. 13A-L and 13A-R show images used for evaluation. Two kinds ofimages, a right-eye image and a left-eye image, were used forevaluation, and each of the images contains four squares (two smallsquares and two large squares).

In the left-eye image and the right-eye image, the large squares aredrawn with different colors. Specifically, a large black square is drawnon the left side of a large white square in the left-eye image (see FIG.13A-L), whereas a large black square is drawn on the right side of alarge white square in the right-eye image (see FIG. 13A-R).

Then, the left-eye image was displayed on a first pixel region for theleft eye and the right-eye image was displayed on a second pixel regionfor the right eye in the display panel 1200, and the images wereobserved under the following conditions.

The images were observed 30 cm away from the center of the display panel1200 in the fabricated 3D display device, from the direct front and frompositions inclined to the right and left from the direct front at anglesup to 14° in 2° increments (see FIG. 13B). The results of observationunder 15 different conditions were recorded using a 3D digital imagesystem 1300 (FinePix REAL 3D W3 manufactured by Fujifilm Corporation).

The 3D digital image system 1300 has two CCD cameras that are distancedfrom each other and provided on either side, and can independentlyrecord an image seen by the left eye and an image seen by the right eyeby using the cameras.

<Evaluation Results>

The fabricated 3D display device followed the position of the viewerevery 50 ms. The angular resolution was 2°. FIG. 14 shows imagesdisplayed by the fabricated 3D display device; the uppermost columnshows the result of observation from the position directly in front ofthe 3D display device, and the underlying columns show the results ofobservation from the positions inclined to the right and left from thedirect front at angles up to 14° in 2° increments.

In the fabricated 3D display device, the image same as that seen fromthe direct front was observed even from the positions inclined to theright and left from the direct front at an angle of 14°. These resultsproved that the area where the viewer can perceive 3D images with thenaked eye was extended.

<Comparative Example>

A parallax barrier optimized for observation from the direct front wasformed by using the fabricated 3D display device. As a comparativeexample, the degree of crosstalk measured 30 cm away from the 3D displaydevice was evaluated while the mode of the parallax barrier is fixed atthe optimized state. That is, the 3D display device exemplified in thecomparative example has a parallax barrier whose mode is fixedregardless of the position of observation.

By the method described in this example, the fabricated 3D displaydevice was evaluated 30 cm away from the center of the display panel1200 in the 3D display device of the comparative example from the directfront and from positions inclined to the right and left from the directfront at angles up to 14° in 2° increments.

<Evaluation Results of Device According to Comparative Example>

FIG. 15 shows images displayed by the 3D display device in thecomparative example; the uppermost column shows the result ofobservation from the position directly in front of the 3D displaydevice, and the underlying columns show the results of observation fromthe positions inclined to the right and left from the direct front atangles up to 14° in 2° increments.

In the case of the 3D display device of the comparative example,significant crosstalk was seen from the positions inclined to the rightand left from the direct front at an angle of 4° or more. The left eyesaw the right-eye image and the right eye saw the left-eye image fromthe positions inclined at an angle of 8° or more. These results showedthat the area where a viewer can perceive 3D images with the naked eyewas small with the 3D display device having a parallax barrier with afixed mode.

This application is based on Japanese Patent Application serial No.2011-054824 and No. 2011-259801 filed with Japan Patent Office on Mar.11, 2011 and Nov. 29, 2011, respectively, the entire contents of whichare hereby incorporated by reference.

1. A display device comprising: a display panel including a first pixelregion for a left eye and a second pixel region for a right eye; aparallax barrier that covers part of the display panel and is variablein a mode; a parallax barrier control circuit configured to control themode of the parallax barrier; an ultrasonic generator, and a pluralityof detectors configured to detect an ultrasonic wave reflected from aviewer, wherein the parallax barrier control circuit controls theparallax barrier in accordance with position of the viewer specified bythe plurality of detectors such that the parallax barrier prevents theright eye of the viewer from seeing the first pixel region and the lefteye of the viewer from seeing the second pixel region.
 2. The displaydevice according to claim 1, wherein the parallax barrier includes aliquid crystal layer sandwiched between a pair of substrates, andwherein at least one of the pair of substrates is provided with aplurality of electrodes for controlling alignment of liquid crystals inthe liquid crystal layer, and each of the plurality of electrodes iselectrically connected to the parallax barrier control circuit.
 3. Thedisplay device according to claim 1, wherein the mode of the parallaxbarrier is a stripe pattern, a checkered pattern, or a crossed pattern.4. The display device according to claim 1, wherein a display elementprovided in the display panel is an organic electroluminescent element.5. The display device according to claim 1, wherein a display elementprovided in the display panel is a liquid crystal element.
 6. A displaydevice comprising: a display panel; a shutter panel including a parallaxbarrier; a control device; an ultrasonic generator, and a plurality ofdetectors configured to detect an ultrasonic wave reflected from aviewer, wherein the display panel, the shutter panel, the ultrasonicgenerator, and the plurality of detectors are connected to the controldevice, and wherein the control device controls the shutter panel tochange a mode of the parallax barrier in accordance with position of theviewer specified by the plurality of detectors.
 7. The display deviceaccording to claim 6, wherein the shutter panel includes a liquidcrystal layer sandwiched between a pair of substrates, and wherein atleast one of the pair of substrates is provided with a plurality ofelectrodes for controlling alignment of liquid crystals in the liquidcrystal layer, and each of the plurality of electrodes is electricallyconnected to the control device.
 8. The display device according toclaim 7, wherein a distance between two electrodes adjacent to eachother is the smallest at a center of the display panel, and wherein thedistance between two electrodes adjacent to each other is the largest ata right end and a left end of the display panel.
 9. The display deviceaccording to claim 6, wherein the mode of the parallax barrier is astripe pattern, a checkered pattern, or a crossed pattern.
 10. Thedisplay device according to claim 6, wherein the shutter panel is anactive matrix shutter panel including a plurality of transistors. 11.The display device according to claim 10, wherein the plurality oftransistors include an oxide semiconductor.
 12. The display deviceaccording to claim 6, wherein a display element provided in the displaypanel is an organic electroluminescent element.
 13. The display deviceaccording to claim 6, wherein a display element provided in the displaypanel is a liquid crystal element.
 14. A method for driving a displaydevice, comprising: transmitting a pulsed ultrasonic wave towards aspace in front of a side where a display surface of the display devicefaces a viewer; specifying a position of the viewer based on a time ittakes for a reflected pulsed ultrasonic wave to be detected by each of aplurality of detectors; specifying a pair of right-eye and left-eyepixels facing a front of the viewer by calculating coordinates where astraight line passing through the position of the viewer orthogonallycrosses the display surface; specifying a distance from the pair ofright-eye and left-eye pixels to the viewer; controlling size of aparallax barrier corresponding to the pair of right-eye and left-eyepixels with reference to the distance from the pair of right-eye andleft-eye pixels to the viewer so that a right eye of the viewer sees apixel for the right eye and a left eye of the viewer sees a pixel forthe left eye; and forming the parallax barrier so that a trapezoid inwhich another pair of right-eye and left-eye pixels is treated as alower base and a light-blocking portion in the parallax barrier thereforas an upper base falls toward the viewer and is further distorted as thetrapezoid is more distant from the pixels facing the front of the viewerin a horizontal direction, and so that the parallax barrier prevents theleft eye of the viewer from seeing a pixel region for the right eye andthe right eye of the viewer from seeing a pixel region for the left eye.15. A method for driving a display device, comprising: transmitting apulsed ultrasonic wave towards a space in front of a side where adisplay surface of the display device faces a viewer; specifying aposition of the viewer based on a time it takes for a reflected pulsedultrasonic wave to be detected by each of a plurality of detectors;specifying a pair of right-eye and left-eye pixels facing a front of theviewer based on the position of the viewer; specifying a distance fromthe pair of right-eye and left-eye pixels to the viewer; controllingsize of a parallax barrier corresponding to the pair of right-eye andleft-eye pixels with reference to the distance from the pair ofright-eye and left-eye pixels to the viewer so that a right eye of theviewer sees a pixel for the right eye and a left eye of the viewer seesa pixel for the left eye; and forming the parallax barrier so that atrapezoid in which another pair of right-eye and left-eye pixels istreated as a lower base and a light-blocking portion in the parallaxbarrier therefor as an upper base falls toward the viewer and is furtherdistorted as the trapezoid is more distant from the pixels facing thefront of the viewer in a horizontal direction, and so that the parallaxbarrier prevents the left eye of the viewer from seeing a pixel regionfor the right eye and the right eye of the viewer from seeing a pixelregion for the left eye.
 16. A method for driving a display device,comprising: transmitting a pulsed ultrasonic wave towards a space infront of a side where a display surface of the display device faces aviewer; specifying a position of the viewer based on a time it takes fora reflected pulsed ultrasonic wave to be detected by each of a pluralityof detectors and an amplitude of the reflected pulsed ultrasonic wave tobe detected by each of the plurality of detectors; and forming aparallax barrier in accordance with the position of the viewer.